Projectiles having a tubular configuration for use in weaponry are known. Tubular configuration of such projectiles provides low drag by minimizing wind resistance. Such tubular projectiles may optionally utilize solid fuel ramjet thrust augmentation. Tubular projectiles utilizing solid fuel ramjet thrust augmentation are required to possess low drag while maintaining sufficient kinetic energy and mass to provide adequate terminal momentum and the consequent destructive force upon impact.
Such solid fuel ramjet tubular projectiles typically comprise a centralized tubular design with an internal mid-section constituting a combustion chamber annularly lined with solid fuel for effecting thrust augmentation. The rear portion of such projectiles is provided with a thrust generating design comprising a constriction portion and a flared rear section, which operate on the hot expanding gases generated in the mid-section combustion chamber in a well-known manner.
Such solid fuel ramjet tubular projectiles are typically shot from a cannon, utilizing a sabot to prevent the exploding gases within the cannon's barrel from escaping through the bore of the solid fuel ramjet tubular projectile. The sabot then detaches from the solid fuel ramjet tubular projectile after the solid fuel ramjet tubular projectile exits the barrel, thus facilitating airflow through the bore thereof.
Explosive charges and/or hardened members may be incorporated into such solid fuel ramjet tubular projectiles to enhance the destructive power and/or penetrating ability thereof.
one such an arrangement which combines the design of a supersonic, low drag tubular projectile with an internally arranged, auto-ignited, solid fuel thrust augmentation system is disclosed in U.S. Pat. No. 5,067,406, issued on Nov. 26, 1991 to Olson et al., and entitled SUPERSONIC, LOW-DRAG, SOLID FUEL RAMJET TUBULAR PROJECTILE, the contents of which are hereby incorporated by reference.
It is well-known that, to effect auto-ignition and a sustained burn, the air flow through the combustion chamber should be subsonic. Moreover, to provide an even burn of the solid fuel, and thereby optimize burn efficiency and projectile stability, the combustion chamber should be relatively narrow in cross-sectional area.
Such solid fuel ramjet tubular projectiles may be either fin or spin stabilized, although spin stabilized solid fuel ramjet tubular projectiles have provided increased accuracy, i.e., an improved ability to strike a target.
Spin stabilization appears to produce poor combustion, resulting in lower than predicted thrust levels. Repeated range tests with the spinning ramjet projectiles have indicated much lower thrust performance than the calculated predictions indicated. This is thought to be due to an internal rotational flow of the air allowing only the outer layer of air to mix with the fuel. This condition would create a fuel rich combustion process through the fully open passageway of the body of the ramjet as the solid fuel ramjet tubular projectile spins in flight resulting in poor combustion efficiency and thus lower thrust levels than desired.
As such, although the prior art has recognized the desirability of providing a solid fuel ramjet tubular projectile, the proposed solutions have, to date, been ineffective in providing a satisfactory remedy.